Woodworkers, cabinetmakers, and craftsmen frequently trim an edge of a workpiece. These workpieces include cabinet doors, entry doors, countertops, etc. composed of materials such as wood, plastics, and man-made solid surface materials such as Corian™. The edge trimming operation typically requires the workpiece's long dimensions (width or length) be reduced by only a few tenths of a millimeter to 10 mm or more.
Edge trimming can be accomplished with the use of various tools or machinery, including, but not limited to, hand planes, powered planes, jointers, radial arm saws, table saws, handheld circular saws, and routers. Each of these tools and methods has inherent disadvantages. For example, hand and powered planes require worker skills to obtain the proper trim-depth and smoothness of cut. Additionally, planes typically cannot edge trim plastics and solid surface materials.
Tools such as jointers, radial arm saws, and table saws are stationary machines that require the workpiece be lifted onto the machinery for trimming. This can be very difficult for handling large workpieces, such as counter tops, and for trimming the width edge of long boards.
Woodworking routers and handheld circular saws are popular tools for performing the edge trimming operation because they are portable, result in a smoothly trimmed edge, and through the use of a guiding device, require lower skills than planes to trim the workpiece. A search of prior art reveals U.S. Pat. No. 6,134,800, a guiding device suitable for assisting in edge trimming. Other guiding device examples are found in woodworking catalogs. An example is a “Clamp ‘N Tool Guide” described by Rockler Woodworking and Hardware, p. 110, consisting of a straightedge clamped to the workpiece to guide the router or handheld circular saw. Woodworker's Supply catalog describes other examples including a “Pro-ftr” available in 0.8 m (30″), 1.4 m (54″) and 2.5 m (99″) lengths on p. 17; a “Multi Angle Cutting Board” on p. 18; and a “Mitermate” on p. 19. The guiding devices heretofore described all suffer from one or more disadvantages:                The guiding device is separate from the router or circular saw and must attach to the workpiece for trimming. Due to inherent size limitations of each guiding device, it may not be capable of trimming oversized workpieces. For example, the 0.8 m (30″) “Pro-ftr” would not be capable of guiding the router for trimming a 1.0 m (40″) long board.        The guiding device is not easily adjusted to obtain accurate and consistent trim cuts. For example, to obtain a 0.25 mm (0.010″) edge trim using the router, a straight router bit and the “Clamp ‘N Tool Guide” requires the guiding device to be set a distance equal to ½ diameter of the router base minus ½ the diameter of the router bit diameter plus 0.25 mm (0.010″) from the edge of the workpiece. This type of precision would not be obtainable using typical woodworking measuring tools such as a ruler or a tape measure.        Each guiding device consists of a straight-edge for guiding the router or circular saw and is not capable of trimming non-straight workpiece edges.        
Edge trimming can be accomplished through use of an external router guide. A search of prior art revealed U.S. Pat. No. 2,672,898. Other external router guides are available from woodworking supply catalogs, including Rockler Woodworking and Hardware, p. 132. These external router guides attach to the router to assist in guiding a router bit for edge trimming. Due to their size and means of attachment, the external router guide is awkward to adjust and use during edge trimming.
Edge trimming can also be accomplished through the use of a self-guided router bit. These bits are readily available from woodworking tool suppliers and are variously described as rabbeting bits, piloted trim bits, pattern flush trim bits, and flush trim bits. Each of these bits uses an upper bearing or lower bearing to assist in guiding during the trimming operation. However, the lower bearing on the piloted, pattern or flush trim bits must contact an already trimmed workpiece surface, or an external guide surface during trimming in order to obtain a proper trim depth of cut. Whereas the rabbeting bit's lower bearing enables it to be self-guiding on an untrimmed workpiece edge, however, after a first trim pass, the bit leaves an uncut workpiece surface. The uncut workpiece surface must be subsequently removed using a handplane, flush trim bit, or by other method to complete the edge trimming operation.
There is a need for a tool for edge trimming, capable of:                Trimming many materials including wood, plastic and solid-surface materials,        Trimming oversized and non-straight edged workpieces,        Being self-guided without the use of external guiding devices,        Being easily and quickly setup to trim to precise dimensions,        Trimming without the need for changing router bits, or requiring the use of another tool or method to complete the operation.        